1. Field of the Invention
The present invention relates to a semiconductor device. For example, the present invention relates to a semiconductor device using materials having low dielectric constant (low-k material) as interlayer insulating film.
2. Description of the Related Art
In semiconductor devices having multi-layer interconnection structure, it is know that low dielectric constant materials are used as an interlayer insulating film in order to reduce interconnection (wiring) capacitance. Generally, in order to realize a material having low dielectric constant such as dielectric constant k not greater than 2.7, the material is formed with pore to have a low density.
The following problems arise if the semiconductor devices having multi-layer interconnection structure are manufactured using a porous film (or low density film having a film density not greater than about 1.5) containing the foregoing pore.
First, a low-k film has low strength; for this reason, there is a possibility that the film cracks during processing. In addition, the shape of via and interconnection formed in the low-k film is fragile in its surroundings, leading the structure to be unstable.
Second, the low-k film has low density; for this reason, there is a possibility that process gas and water content permeate from the side of a via hole formed in the film. As a result, the permeated gas desorbs in the film; therefore, this affects the next process.
Thirdly, the low-k film receives damage by dry process such as RIE (reactive ion etching) and ashing, used for processing contact holes and interconnection trenches.
The damage given to the low-k film means a state that the original bond of the low-k film is broken down. For example, in a SiOCH-based low-k film, Si—CH3 and Si—C bonds are broken. As a result, Si-dangling bond is formed, or Si—OH and Si—NH are formed. In the portion having received the damage, the bond is broken; as a result, C (carbon) concentration is reduced. With the reduction of C concentration, the film density is also reduced; for this reason, the portion readily absorbs process gas and water content. The absorbed water content and gas diffuses in the low-k film. This affects the electrical characteristics of the low-k film. More specifically, the effective electric constant of the low-k film increases, leak current is induced between interconnections in the film, and Time Dependent Dielectric Breakdown (TDDB) occurs. These are factors of reducing breakdown voltage reliability. The gas remaining in the low-k film desorbs, and thereby, other films are peeled off. The damaged region having reduced C concentration may be melted due to HF and NHF3-based chemical liquids frequently used in the process of manufacturing the semiconductor device. For this reason, it is difficult to achieve dimension control on the surroundings of the damaged region.